SuperFetch is a performance enhancement introduced in [[Microsoft]] [[Windows|Windows Vista]] to reduce the time necessary to launch applications. An expanded version of the [[Prefetch]] files found in Windows XP, they record usage scenarios and load resources into memory before they are needed. Those resources can be loaded into physical memory and extra memory provided by [[ReadyBoost]].

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== File header ==

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The file header is 84 bytes of size and consists of:

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{| class="wikitable"

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|-

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! Offset

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! Size

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! Value

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! Description

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|-

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| 0

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| 4

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| 0x304D454D ("MEM0") or 0x4F4D454D ("MEMO")

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| Signature

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|-

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| 4

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| 4

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|

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| Uncompressed (total) data size

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|-

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|}

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== Configuration ==

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== Compressed blocks ==

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The file header is followed by compressed blocks:

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Because SuperFetch appears to leave a system with no available memory, some users turn it off to create the appearance of having more free memory. The feature can be configured by changing the <tt>HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters\EnableSuperfetch</tt> [[Registry]] key [http://www.codinghorror.com/blog/archives/000688.html]. A value of zero disables SuperFetch, one enables it for booting only, two for applications, and three for both applications and boot. This setting can also be changed using the Services console, <tt>services.msc</tt> [http://tiredblogger.wordpress.com/2007/03/27/superfetch-not-so-super-for-gaming/].

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{| class="wikitable"

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|-

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== File Formats ==

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! Offset

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! Size

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Data for SuperFetch is gathered by the <tt>%SystemRoot%\System32\Sysmain.dll</tt>, part of the Service Host process, <tt>%SystemRoot%\System32\Svchost.exe</tt>, and stored in a series of files in the <tt>%SystemRoot%\Prefetch</tt> directory [http://www.microsoft.com/technet/technetmag/issues/2007/03/VistaKernel/]. These files appear to start with the prefix <tt>Ag</tt> and have a <tt>.db</tt> extension. The format of these files is not fully known, there is available unofficial partial specification [http://blog.rewolf.pl/blog/?p=214] and open source (GPL) dumper for .db files [http://code.google.com/p/rewolf-superfetch-dumper/]. Some information can be gleaned from these files by searching for [[Unicode]] [[strings]] in them.

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! Value

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! Description

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The SuperFetch feature is seeded with some basic usage patterns when the operating system is installed [http://channel9.msdn.com/showpost.aspx?postid=242429].